It's a digi World! #30

Here, both the inputs are X and hence the product of X twice will also be X and apply complement to it and hence the answer NOT X......

This is the representation of NAND gate with the AND gate working first and then NOT gate acting on the result of AND gate to give the final value of NAND gate. Here, both the inputs of NAND gate are $X$ .

The AND gate is such a gate which requires both inputs to be the HIGH / ON value (here considered $X$ ) to give an output equal to that HIGH / ON value. The NOT gate simply provides output as the negation result of its input.

Now, in this diagram, when both inputs of NAND gate (combination of AND and NOT gate) are $X$ , i.e, the HIGH value, then the output of the AND gate part is also $X$ . Then, this ouput goes through NOT gate which simply gives the negation ouput, i.e., "not $X$ ". Thus, the NAND gate completes giving the output as "not $X$ ".

So, the answer is Not X.